1. Field of the Invention
This invention relates to a method of treating wool scouring liquor effluent to render it suitable for recycling or discharge and to concurrently recover wool grease as a by-product.
2. Description of the Prior Art
The scouring of raw wool produces a liquor which contains varying amounts of woolgrease, suint, dirt, vegetable and faecal matter, fine wool fibre and detergent. The liquor is highly polluting because of the high level of solids, the large oxygen demand of the suint and the presence of the grease which has a high BOD and is not readily biodegradable.
The grease (technically a wax) consists of fatty acids and complex monohydric alcohols. The alcohols are sterols, triterpene alcohols and wax alcohols. The major constituent is cholesterol which accounts for 30-40% of the unsaponifiable material in the woolgrease. The fatty acids are derived from four main series -- the normal fatty acids, the iso-acids, the branched-chain acids and hydroxy acids.
Suint is the water soluble material on the wool and consists largely of salts sweated by the sheep. Soluble salts of carboxylic acids make up 65% of the constituents of suint which also contains minor amounts of lactic, hippuric and succinic acids, urea and lanaurin, a bile pigment which gives suint its characteristic brown-red colour.
The removal of grease from scour liquor is advantageous because the grease is of commercial value, its removal increases the useful life of the scour liquor and grease removal reduces the pollution load of effluent discharged from a scour plant and renders it more amenable to further treatment. Many different techniques have been developed for the removal of grease from scour liquor, and of these the most common is the use of continous sludge discharge centrifuges. After being fed through a settling tank or hydrocyclone to remove heavy solids the scour liquor is passed through a centrifuge which removes as a cream the grease mixed with water. The cream after heating and storage can be separated with a simple disc separator.
The oldest method of removal and one still in use is acid cracking. Sulphuric acid is added to the scour liquor to adjust the pH to 3.5 at which it cracks and the grease-rich phase is removed by filtration or flotation and the residual liquor is neutralised and discharged. A low quality grease may be extracted from the sludge removed from the liquor, however, as the cracking is only suitable for non-detergent scouring systems.
Also widely practiced is the use of salts such as ferrous sulphate, alum and calcium chloride to crack the grease/water emulsion. It is difficult to recover the grease from the sludge formed by these methods.
In British Patent 1,112,596 of Mosilana, Vlnarske Zavody, Narodni Padnik, a Czechoslavakian body corporate, which was published on May 8, 1968, there is disclosed and claimed a method for recovery of wool grease from spent wool scour liquor. The method comprises mixing spent scouring liquor while maintaining the original pH value with 1 to 10% by volume of an aliphatic or cyclic alcohol with 6 to 8 carbon atoms in the molecule, mechanically separating the aqueous phase which has been substantially freed from wool grease and recovering the wool grease from the alcoholic phase in the two phases. The phases are normally separated by a centrifuge. Alcohols with up to five or nine or more carbon atoms may not be employed in the process because the wool grease would remain in emulsion and could not be separated.